Focusing device for volatile and semivolatile organic compounds in the gaseous phase

ABSTRACT

A focusing device for volatile and semi-volatile organic compounds in the gaseous phase, comprising a support structure, a container for said organic compounds, a cooling element and a heating element for their transfer to the analysis system, characterized in that said cooling element and said heating element are positioned in two separate regions of said support structure and form a single block movable relative to said container.

[0001] This invention relates to a focusing device for volatile and semivolatile organic compounds in the gaseous phase.

[0002] Focusing traps used in analytical instrumentation, in particular for gas chromatography, are known for concentrating the volatile and semi-volatile compounds present in a gaseous phase, before transferring them to an analysis system.

[0003] Said organic compounds are concentrated by cooling the focusing trap, and are transferred to the analysis system by heating the trap.

[0004] With known focusing traps, during their operation the heating system and cooling system are in a fixed position relative to the trap, which can be heated only on termination of the preceding cooling stage.

[0005] A drawback of known focusing traps is that their applicational performance, which is greater the faster the passage from low temperature (concentration stage) to high temperature (transfer stage), is limited by the limited trap heating rate, related to the rate of temperature rise of the heater, which has to start from cold and hence requires several seconds to reach and stabilize itself at the predetermined temperature.

[0006] Another drawback is the possible presence of interactions between the heating element and the cooling element.

[0007] According to the invention these drawbacks are overcome by a focusing device for volatile and semi-volatile organic compounds in the gaseous phase as described in claim 1.

[0008] A preferred embodiment of the invention is described in detail hereinafter with references to the accompanying drawings, in which:

[0009]FIG. 1 is a schematic view of the focusing device of the invention in the cooling condition, and

[0010]FIG. 2 shows it in the heating condition.

[0011] As can be seen from the figures, the device of the invention comprises a support structure 2 provided with parallel columns 4, supported at their ends by two plates 6, 6′.

[0012] By means of suitable connectors 8, 8′, the two plates 6, 6′ support a tube 10, the central portion 12 of which constitutes the “trap” for the organic compounds to be analyzed.

[0013] In the interior of the structure 2 there is provided, slidable along the columns 4, a block 14, to which an electric heater 16 and an electric cooler 18 are applied.

[0014] Said block 14 is driven to and for along the columns 4 by a connecting rod and crank system, which does not form part of the invention and is simply cited herein without being shown in the drawings.

[0015] The position of the heater 16 and of the cooler 18 relative to the block 14 is such that in one of the end positions of this latter the trap 12 is surrounded by the cooler 18, whereas in the other it is surrounded by the heater 16.

[0016] The device of the invention operates as follows: initially, the block 14 is disposed such that the cooler 18 surrounds the trap 12 (see FIG. 1) and can cool the organic compounds contained within it, to condense them. At the same time, the heater 16, which is also powered so as to have already attained the predetermined working temperature, is laterally displaced from the trap 12.

[0017] When the trap has been cooled on the basis of the scheduled working cycle, the block 145 is slid along the columns 4 so that the heater 16 faces the trap 12 (see FIG. 2) so that the heater, already at its working temperature, heats the organic compounds contained in the trap with the necessary rapidity.

[0018] On termination of this stage the heated organic compounds are transferred to the gas chromatograph.

[0019] From the aforegoing it is apparent that as the trap passes from the cooling stage to the heating stage, not statically by electrically activating/deactivating the two elements 16, 18 provided for this purpose, but instead dynamically by moving these latter, which are always maintained at their working temperature, the trap is able to attain the predetermined operating conditions more rapidly. In particular, heating of the trap 12 is faster, especially during the initial stage immidiately after the cooling stage, because when the trap comes face to face with the heater, this is already thermally stabilized at the set temperature.

[0020] By virtue of this rapid heating, transfer to the analysis system is more effective and rapid.

[0021] Moreover, with the device of the invention there is no thermal interaction between the heating element and the cooling element. 

1. A focusing device for volatile and semi-volatile organic compounds in the gaseous phase, comprising a support structure (2), a container (12) for said organic compounds, a cooling element (18) for their concentration and a heating element (16) for their transfer to the analysis system, characterised in that said cooling element (18) and said heating element (16) are positioned in two separate regions of said support structure (2) and form a single block (14) movable relative to said container (12).
 2. A device as claimed in claim 1, characterised in that the structure (2) comprises guide means (4) for a block (14) movable between two end positions, at which said cooling element (18) and, respectively, said heating element (16) face said container (12).
 3. A device as claimed in claim 1, characterised in that the structure (2) comprises a plurality of parallel columns (4) supported at their ends by two plate elements (6, 6′), said block (14) being associated with means for its movement in the two directions along said columns (4).
 4. A device as claimed in claim 3, characterised in that said plate elements (6, 6′) support, by means of connectors (8, 8′), a tubular element (10), the central portion (12) of which forms the container (12) for said organic compounds.
 5. A device as claimed in claim 4, characterised in that said heating element (16) and said cooling element (18) are shaped such as to enclose said tubular element (10). 